Adder description

The adder (Vipera berus) is an extremely widespread reptile, and is the UK’s only venomous snake. As a result of its venomous bite, the adder is a much-maligned species in most of its range, with a wealth of folklore surrounding it (4). However, despite the public perception of this snake, it is generally a shy, timid and non-aggressive species (5).

A stocky snake, the adder is easily identified by the dark zigzag line passing along the back bordered by rows of spots. A dark mark which takes the form of an 'X', 'V' or 'H' is located on the rear of the angular head and the pupil is vertical (3).

Males are greyish, whitish, pale yellow or cream in colour with very dark contrasting markings, whereas females are typically a brownish or reddish colour with brown markings (2). Females also tend to be longer and wider than males, and have shorter tails. Male and female juveniles are reddish in colour (3).

In all cases, the belly is grey, greyish-brown or bluish, and the throat is dirty yellow or white. Completely black (melanistic) adders arise quite frequently (3).

Related species

Adder biology

The adder is typically active during the day, when it hunts mainly for small mammals, including voles, shrews and mice. Grasshoppers and locusts, lizards, young birds and frogs may also be taken (8). In warm conditions, the adder will actively hunt its prey, but it often uses a ‘sit and wait’ technique. The adder strikes prey animals with its fangs to inject venom, then releases the prey and follows the scent trail it leaves behind. Upon finding the dying or already dead animal, the adder begins to swallow it head first (3).

The adder emerges from hibernation in March, with males emerging before females (3). For the first few weeks after emergence, this species remains fairly inactive and spends much of its time basking (8). After the male has shed its skin in April it becomes more active, and will begin to search for potential mates by following scent trails. The female sheds its skin a month later than the male, and both sexes shed again later on in summer. The adder does not feed until after it has mated, and so during the time before mating, both the male and female adder live off fat reserves that are built up during the previous year (3).

Upon discovering a receptive female, the male begins a courtship display in which the tongue is flicked over the female’s body. The male and female may vibrate their tails briefly and bouts of body quivering may ensue. If the courtship is a success, copulation takes place, after which the pair may remain together for two hours or so. If another male approaches the pair at any point, the first male will defend the female aggressively, and a fight may result (3). These fights are known as ‘the dance of the adders’ as the males partly raise their bodies off the ground and may become entwined, often repeatedly falling to the ground and rising up again. More than two males may be involved in such a contest (4).

The female adder usually reproduces once every two years, returning to the site of hibernation towards the end of August or early September to give birth. The adder is viviparous, giving birth to between 3 and 18 live young which are initially encased in a membrane (7). After giving birth the female must feed intensively in order to build up sufficient reserves for hibernation(3). The young adders do not feed until the following year, but live off the yolk sac and fat reserves that they are born with. The adder reaches sexual maturity at three to four years of age (3).

The adder usually enters its hibernacula in September or October (3). Hibernacula are often the abandoned burrows of small mammals typically located on high, dry ground or the overgrown root systems of fallen trees. The adder usually uses the same hibernation site for life (9).

Although adders are poisonous, they are not aggressive and rarely bite humans or domestic animals, preferring to retreat into thick vegetation instead. Most adder bite incidents result when they are picked up or trodden upon, and in most cases they are not serious. The elderly, the very young or people in ill health are at most risk (3).

Adder range

In Britain, the adder has a rather patchy distribution. It is more numerous in southern England than the north, is not common in the Midlands, but is fairly numerous in west Wales and southwest England. It is widespread in Scotland but is absent from the Outer Hebrides, the Central Lowlands and the Northern Isles. It is absent from Ireland (3)(5)(6).

The adder has the widest global distribution of all terrestrial snakes; it is found in the west from Britain and Scandinavia to central France, reaching eastwards as far east as the Pacific coast of Russia and Korea, and is the only snake to occur in the Arctic Circle (3).

Adder habitat

The adder is found in a range of habitats including open heathland, woodland, moors, lake sides, alpine rocky slopes, and saline and sandy semi-deserts. It requires sunny glades or slopes where it can bask and dense cover in which to take shelter (7)(8).

Species found in a similar habitat

Adder status

Adder threats

The adder is threatened by habitat loss in a number of areas throughout its European range. The open habitats it needs, particularly heathland, has been locally lost as a result of scrub encroachment, development, agriculture and afforestation (1).

A further threat to the adder is the persecution of this species by humans, and potentially collection for the pet trade. In Romania, the adder is threatened by illegal collection for its venom (1). However, the exceptionally wide distribution of this species, combined with its tolerance to a very large variety of habitats, mean that this species is not currently threatened on a global scale.

Adder conservation

The adder is listed on Annex III of the Bern Convention, which aims to conserve wild flora and fauna and their natural habitats (10). It also occurs in a number of protected areas throughout its range, and is protected by national legislation in many range countries (1).

In the UK it is illegal to kill, injure, harm or sell adders under the Wildlife and Countryside Act, 1981 (11). The adder is classified as a priority species under the UK Biodiversity Action Plan (UK BAP) (12), and is featured in a number of Local Biodiversity Action Plans. An important proposed action is to educate the public about this species to dispel the fears and prejudice surrounding it and reduce its deliberate persecution (12).

There is a need to conserve separate evolutionary lineages of the adder, as some may represent currently unrecognised species (1).

Authentication

Glossary

Hibernacula

Sites where hibernation (A winter survival strategy in which an animal’s metabolic rate slows down and a state of deep sleep is attained) takes place.

Hibernation

A winter survival strategy characteristic of some mammals in which an animal’s metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is ‘diapause’, a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.

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